1. Technical Field
This invention relates generally to semiconductor devices which include a plurality of stacked semiconductor die, and more particularly, to constructing such a device with improved performance and yield.
2. Background Art
FIG. 1 illustrates a multi-die semiconductor device 40 (shown in simplified form), with the die in stacked relation. As shown in FIG. 1, a carrier substrate 42 has a chip attach surface 44. A semiconductor chip or die 46 is attached to the surface 44 of the substrate 42 by a die bond. A spacer 48 is attached to the die in stacked relation by a die bond, and a semiconductor die 50 is attached to the spacer 48 in stacked relation by a die bond. A semiconductor die 52 is attached to the die 50 in stacked relation by a die bond. Using standard wire bonding techniques, wires 53, 54, 55 connect bond pads 56, 58, 60 on the respective die 46, 50, 52 with bond pads 62 on the substrate 42.
As will be seen in FIG. 1, the spacer 48 is of smaller dimensions, i.e., smaller length and width, than the die 46 and the die 50, and the spacer 48 is centered on the die 46 therebelow and with relation to the die 50 thereon (see FIG. 2). This provides access to the bond pads 56 on the die 46 for wire bonding of the die 46 to the substrate 42. This also results in the die 50 on the spacer 48 overhanging the spacer 48 as shown. With the die 50 being relatively large (for high device performance), the overhang indicated as of dimension A can be relatively large. Connection of the wires 54 to the bond pads 58 on the die 50 involves a relative large impact (downward, FIG. 1) by the bonding head on the die 50 on that overhanging portion which can cause the overhanging portion of the die 50 to bounce and vibrate. It will be seen that a large dimension A (resulting in turn in a large lever arm dimension B) as shown in FIG. 1 can result in a relatively large bounce, as the lever arm on which force is applied at the bond pads 58 on the die 50 is relatively large. This excessive bounce can result in imperfect wire bonding, in turn resulting in reduced yield of manufactured devices.
FIG. 3 illustrates another multi-die semiconductor device 60 (again shown in simplified form), with the die in stacked relation. As shown in FIG. 3, a carrier substrate 62 has a chip attach surface 64. A semiconductor chip or die 66 is attached to the surface 64 of the substrate 62 by a die bond. A semiconductor die 68 is attached to the die 66 in stacked relation by a die bond. Using standard wire bonding techniques, wires 70, 72 connect bond pads 74, 76 on the respective die 66, 68 with bond pads 78 on the substrate 62.
FIG. 4 is a plan view of the device of FIG. 3. As shown, the plurality of wires 70 connect the bond pads 74 on the die 66 with bond pads 78 on the substrate 62, the other plurality of wires 72 connect bond pads 76 on the die 68 with bond pads 78 on the substrate 62. Due to the complexity of the device, including the large number of bond pads on the die and substrate (much greater than the number illustrated), wire crossings occur (FIG. 4), resulting in increased likelihood of shorting and consequently failure of the device.
Therefore, what is needed is an approach wherein device yield is improved by reducing the bounce and shorting problems described above.